This invention relates to a system for controlling ultrafiltration in hemodialysis. More particularly, it relates to the control of ultrafiltration in a closed hemodialysis system.
Hemodialysis is a technique of removing certain toxic wastes from the human body in cases of renal failure by the use of an artificial kidney in conjunction with an associated machine. The patient's blood is temporarily brought outside of the body by tubes and permitted to pass by at least one semipermeable membrane, which may be a group of hollow fibers, in the artificial kidney, also called a dialyzer. The semipermeable membrane separates the blood from dialysate solution. The impurities from the blood pass through the membrane and into the dialysate solutions primarily by osmotic pressures. The cleansed blood is then returned to the body. During this procedure it is also necessary to remove excess fluids from the body. This is accomplished by a technique known as ultrafiltration. The amount of ultrafiltrate which is removed from the body is normally controlled by pressure across the semipermeable membrane. This transmembrane pressure is the result of the differential between the blood pressure and the pressure which exists on the dialysate side of the membrane. A description of an ultrafiltration system in a closed dialysis system is set forth in U.S. Pat. No. 3,669,880 assigned to the assignee of the present invention and which is hereby incorporated by reference.
One of the problems associated with prior art ultrafiltration control systems has been a lack of accuracy because of the differing characteristics of each dialyser which is used for each dialysis treatment. In particularly, the rate of passage of ultrafiltrate through the semipermeable membrane will differ for dialyzers from different manufacturers as well as those of the same manufacturer. Applicant has overcome this problem of inaccuracy with the present invention.
In general there are two types of hemodialysis systems. One type is referred to as a single pass system whereby the dialysate solution passes through the dialysate compartment of the dialyzer only once and then is discharged as waste. The single pass system obviously requires a great deal of fluid to fully treat the patient. A second type of system, and the system which is referred to in the previously mentioned U.S. Pat. No. 3,669,880, is a closed system. The closed system may utilize a filter such as an ion exchanger, for example, a zirconium phosphate column together with charcoal and other materials, to regenerate the used dialysate solution and pass the regenerated solution across the membrane over and over again until the treatment has been completed. While the system of the present invention has been specifically designed for use in a closed system, with minor modification it could be utilized in a single pass system.